1. Technical Field
The present invention relates to a method of manufacturing a liquid developer, a liquid developer, and an image forming apparatus.
2. Related Art
As a developer for developing an electrostatic latent image formed on a latent image carrier, there are known two types of a dry toner that is formed of a material containing a colorant, such as a pigment or the like, and binder resin and is used in a dry condition thereof, and a liquid developer that is obtained by dispersing toner particles into a carrier liquid having electric insulation properties.
The dry toner is generally manufactured by a dry milling method that mills a material containing a colorant and a binder resin in a dry condition. In such a dry toner, since the solid state toner is handled, there is an advantage in handleability thereof. Meanwhile, there are many problems in view of an adverse affect of toner powder on a human body, contamination by dispersion of toner, and uniformity when the toner is dispersed. Further, in such a dry toner, since aggregation of toner particles is likely to occur upon preservation or the like, it is difficult to obtain toner particles each having a sufficiently small size. Further, it is difficult to form a toner image with high resolution. In addition, when the sizes of the toner particles are comparatively small, the above problems by the toner powder drastically appear.
Meanwhile, in the liquid developer, since an insulating liquid is used as a medium, the problem, such as aggregation of toner particles in the liquid developer upon preservation rarely occurs, compared with the dry toner, and thus fine toner particles can be used. As a result, the liquid developer has such advantages as good reproducibility of an image having thin lines, good gray-scale reproducibility, and excellent color reproducibility, compared with the dry toner. Further, the liquid developer is also superior as a method of forming an image at high speed.
As a method of manufacturing such a liquid developer, in JP-A-8-36277, there is disclosed a wet milling method that mills a material containing a colorant and a resin in an electric insulation liquid to thereby manufacture a liquid developer. Further, in JP-B-8-7470, there is disclosed a polymerization method that polymerizes monomer ingredients in the electric insulation liquid to thereby form resin particles insoluble to the electric insulation liquid.
However, a known method of manufacturing a liquid developer suffers from the following problems.
That is, in the wet milling method, it is difficult to mill toner particles to have a sufficiently small size. Further, since it takes much time and considerable energy for milling to obtain the toner particles each having a sufficiently small size, productivity of the liquid developer is drastically degraded. Further, in the above-described method, the particle size distribution of the toner particles is likely to be widened (a variation in particle size is large) As a result, a variation in characteristic between the toner particles (for example, charging property or the like) is likely to be increased. Meanwhile, although the above-described dry milling method can be considered, in this case, it is difficult to obtain fine particles required for the toner particles of the liquid developer. In addition, since aggregation is likely to proceed, it is difficult to obtain comparatively small toner particles.
Further, in the polymerization method, it is difficult to establish an appropriate polymerization reaction condition. Accordingly, it is difficult to generate a resin material having an appropriate molar weight, to form toner particles each having a desired size, or to sufficiently reduce a variation in size between the toner particles. As a result, quality stability and reliability of the toner, such as charging property or the like, is likely to be degraded. Further, in the polymerization method, it takes comparatively long time to form toner particles, and thus productivity of the liquid developer deteriorates. In addition, in the polymerization method, large production apparatuses and large production equipment are generally needed.
Further, in the known methods described above, it is difficult to obtain a liquid developer in which dispersibility of the toner particles is sufficiently high. If dispersibility of the toner particles is bad, when the toner particles are left for a long time, the toner particles may be subsided, and aggregation of the toner particles may occur. Further, once if the toner particles are subsided and aggregation occurs, even though the toner particles are stirred again and dispersed, it is difficult to disperse the toner particles. Accordingly, upon image forming, the toner particles cannot be uniformly supplied.